Key clinical point: DW-MRI is the gold standard for imaging, but CTP is more widely available.

Major finding: Rates of neurologic deterioration in hospital, symptomatic intracranial hemorrhage, and death related to stroke were similar regardless of whether CT or MR imaging was used to assess patients’ infarcts.

LOS ANGELES – The benefits of mechanical thrombectomy observed in the DAWN trial for patients with acute ischemic stroke and a mismatch between core imaging and clinical presentation out to 24 hours appear to apply regardless of whether their eligibility is determined by CT perfusion or diffusion-weighted magnetic resonance imaging, according to a subanalysis of the trial data.

Diffusion-weighted magnetic resonance imaging (DW-MRI) is considered the gold standard, but it is not as widely available as CT perfusion (CTP) and previous studies have shown that MR is associated with longer times between stroke onset and treatment randomization. “Though MR was originally preferred in DAWN, it was pretty clear that CT perfusion was going to need to be employed in the trial as well,” Cathy Sila, MD, said during her presentation of the results of the subanalysis at the International Stroke Conference 2018, sponsored by the American Heart Association.

The research sought to determine if the two imaging methods perform similarly. CTP is more readily available, but it has some issues. In patients with severe heart failure, a severe proximal stenosis, or a contralateral severe stenosis, the technique may struggle to accurately image the core infarct, which has led some to wonder if the outcomes would be as good using CTP as selection criteria. “In our institution, we’ve had this conversation very frequently,” said Dr. Sila, who is a vascular neurologist and the director of the University Hospitals Systems stroke program in Cleveland.

To be eligible for DAWN, the core infarct had to correspond to at least a 30% decrease in regional blood flow in the CTP map, or an apparent diffusion coefficient of less than 620 on DW-MRI.

The researchers included all 206 patients in the DAWN study (N Engl J Med. 2018;378:11-21), separating them into DW-MRI or CTP groups based on which imaging method was used to randomize them during the trial. There were no statistically significant differences in any of the baseline characteristics between the two imaging groups.

The 26 sites participating in DAWN had clear differences in their preferences for imaging techniques; 19 exclusively used CTP, 4 used only DW-MRI, and 3 sites used a combination of both imaging methods.

There were no statistically significant differences between the two groups in any of the measured clinical outcomes, including neurologic deterioration in hospital (22.8% with CTP vs. 15.7% with DW-MRII, P = .286), symptomatic intracranial hemorrhage (4.1% with CTP vs. 4.8% with DW-MRI, P = 1.000), or death related to stroke (19.5% with CTP vs. 13.3% with DW-MRI, P = .263). Outcomes at 90 days proved to be similar between CTP and DW-MRI for achieving functional independence (29.3% vs. 34.9%, respectively; P = .445) and utility-weighted modified Rankin Scale scores (4.2 vs. 4.9, respectively; P = .172).

Multivariate analyses showed that 90-day functional independence was predicted by thrombectomy treatment, age, blood glucose level, baseline National Institutes of Health Stroke Scale score, and core lab ASPECTS (Alberta Stroke Program Early CT Score), but not the method of imaging.

“The efficacy and safety of mechanical thrombectomy for patients meeting those clinical mismatch criteria at 6-24 hours were comparable whether the small core infarcts were measured by diffusion imaging or cerebral blood flow imaging. I believe that future clinical trials aiming to extend the eligibility outside of this prespecified population should include both imaging modalities to determine whether these results are generalizable,” Dr. Sila said.

The DAWN study was funded by Stryker Neurovascular. Dr. Sila has reported receiving honoraria from Medtronic.